1. Field of the Invention
The present invention relates to an optical fiber transmission-type laser processing apparatus.
2. Description of the Related Arts
In case of performing a laser processing at a site remote from the body using a laser processing apparatus such as a YAG laser, an input unit within the apparatus body is linked via an optical fiber with an output unit at remote site (processing site). A laser beam generated in the apparatus body is transmitted from the input unit through the optical fiber to the output unit, where the laser beam is projected onto a workpiece.
Recently prevailing is a multi-position processing in which a laser beam oscillated within the apparatus body is branched into a plurality of laser beams, which are then directed via optical fibers toward different positions.
A laser processing apparatus generating a pulsed laser beam to perform the laser processing has hitherto used a technique for variably controlling waveforms of a laser output of the pulsed laser beam or of predetermined electric parameters corresponding thereto, so as to be adaptable to a diversity of processing demands.
According to such a waveform control system, a desired reference waveform for waveform control is previously set and entered into the laser processing apparatus. In the laser processing apparatus, a laser oscillation unit is supplied with a power from a laser power supply unit to oscillatorily output a laser beam, and a laser control part controls the laser power supply unit with an open loop control system or a closed loop (feedback) control system so as to allow waveforms, that is, variations with time of the laser output of the laser beam oscillatorily output from the laser oscillation unit or of predetermined electric parameters of the laser power supply unit to conform to that reference waveform.
In case of the laser processing using the pulsed laser beam, typically a series of pulsed laser beams are irradiated to the workpiece at a preset repetition frequency.
In the optical fiber transmission-type laser processing apparatus as described above, the laser beam must impinge correctly on one end surface of the optical fiber (in other words, it must be concentrated onto the central portion of the end surface) in the input unit of the apparatus body. Inaccurate incidence of the laser beam on the optical fiber results in a greater loss of laser output or in burning of the end surface of the optical fiber. Thus, in the input unit, upon the assembling or setting of the apparatus or upon the exchange of the optical fibers, the position of a condenser lens is adjusted (focused) in the optical axis direction (Z direction) while simultaneously the attachment position of the optical fiber is adjusted (optical axis aligned) in the direction (XY direction) orthogonal to the optical axis direction.
In this type of laser processing apparatus, however, if the laser output exceeds a certain value, the thermal lens effect or the like of the laser medium (YAG rod) may possibly cause as shown in FIG. 22 an enlarged beam diameter or output angle as indicated by a dotted line LB' of the laser beam LB oscillated from the laser oscillation unit 200, with the result that the laser beam overfill the incidence end surface of the optical fiber 204 even though it is condensed by the condenser lens 202 in the input unit, consequently bringing about a possible burning of the optical fiber 204 or defective processing. The limit value of the laser output causing such a deficiency depends on the type and diameter of the optical fiber.
For this reason, in the multi-position processing system, any change in the type or diameter of the fibers due to the replacement of the optical fibers may result in a change of upper limit of the laser output for the optical fibers. Therefore, even though it has been normal so far, the upper limit may be exceeded after the exchange, resulting in a damage of the optical fibers.
Furthermore, in the waveform-controlled laser processing apparatus, the user (operator) can set the pulse waveform and the pulse repetition frequency of the pulsed laser beam to any values. As a result, there may possibly be made such a setting as to exceed the laser output limit value for the optical fiber.